Brefeldin A causes severe dilation of ER membranes in primary CLL cells prior to the onset of apoptosis. (A) Primary CLL cells were treated with 10 μM F-ara-A or 30 ng/mL (107 nM) and 100 ng/mL (357 nM) BFA for 24 hours. Cells were fixed and ER morphology was analyzed by transmission electron microscopy as described in “Patients, materials, and methods.” Original magnification of all images is indicated. Images were obtained as for Figure 1A-B. (B) Brefeldin A induces changes in ER morphology prior to the onset of appreciable apoptosis. A portion of BFA-treated primary CLL cells used for transmission electron microscopy analysis was fixed for active caspase-3 staining to quantitate the percentage of apoptotic cells. Only a minor portion of brefeldin A-treated cells stained positively for caspase-3 at this time point (24h). Error bars indicate the standard deviation (n = 4).